Various vehicular tires have been proposed which are composed of, or contain a component composed of, polyurethane. The polyurethane is typically the reaction product of an organic polyisocyanate and polymeric polyol which contains a slight molar excess of the polyisocyanate in the reaction mixture to allow for the presence of very small amounts of impurities, including moisture, which might be present with which the polyisocyanate is reactive.
In one embodiment, the polyurethane for this invention is desirably a cast polyurethane in a sense of being the product of casting a liquid polyurethane reaction mixture into a suitable mold cavity to form the molded polyurethane product without being sulfur or peroxide cured. Such cast polyurethane desirably does not contain an unsaturated hydrocarbon component.
A cast polyurethane is intended to be distinguished from a millable polyurethane composed of a product of a polyurethane reaction mixture containing unsaturated hydrocarbon component(s) cured polyurethane which is thereby sulfur curable to yield a sulfur or peroxide cured polyurethane.
Exemplary of such tires composed of or containing polyurethanes are, for example, and not intended to be limitive, U.S. Pat. No. 4,095,637 relating to a solid polyurethane tire/wheel assembly and U.S. Pat. Nos. 4,295,513, 4,131,667 and 8,662,122 in general.
In practice, tires are generally subject to dynamic flexing during their service and operation. For tires which are composed of or which contain a component comprised of, polyurethane, it is generally considered as being important to provide a degree of resistance to cut growth propagation for the polyurethane.
For this invention, it is proposed to use rubber reinforcing carbon black for providing reinforcement for the polyurethane in a sense of providing a degree of cut growth propagation resistance for the polyurethane.
For rubber tires, particulate reinforcement in a form of rubber reinforcing carbon black has often been used for various rubber compositions for rubber tire components. However, rubber reinforcing carbon black for reinforcement of rubber compositions is dusty in nature and is therefore conventionally commercially provided as compacted carbon black in a form of pellets thereof for addition to rubber compositions instead of dusty un-compacted carbon black. During high shear mixing of the compacted carbon black pellets in the highly viscous rubber composition, the carbon black pellets are broken down to their very small carbon black aggregates to provide carbon black reinforcement of the rubber composition. For example, see U.S. Pat. Nos. 6,800,126, 7,247,669, 3,294,733, 3,298,984, 3,317,458, 3,345,324, 3,491,052, 3,767,605 and 3,923,707.
However, mixing of a liquid polyurethane reaction mixture is conducted under low shear mixing conditions which is considered as being insufficient to break down the carbon black pellets to small carbon black particles, or aggregates.
Therefore, for the practice of this invention, pellets of compacted carbon black are pulverized into small carbon black granules which are then mixed with the polymeric polyol component of a polyurethane reaction mixture. It is proposed to use the pulverized rubber reinforcing carbon black as being a chemically interactive particulate reinforcement for a polyurethane component of a vehicular tire. It is considered that such pulverized rubber reinforcing carbon black presents a particular advantage for providing reinforcement of polyurethane for a tire or tire component. Such advantage relates to the pulverized rubber reinforcing carbon black surface as containing numerous isocyanate reactive groups which can combine chemically with the aforesaid excess isocyanate groups contained in a polyurethane reaction mixture to create covalent linkages between the carbon black and isocyanate of the polyurethane reaction mixture, perhaps also in a sense of crosslinking, which can thereby provide reinforcement for improvement of various physical properties of the polyurethane. Representative of various isocyanate reactive groups which can reside on the surface of the pulverized carbon black are, for example and not intended to be limiting, hydroxyl groups, carboxylic acid groups, and quinones.
Affinity of the carbon black with the polyurethane can depend upon accessibility and reactivity of such isocyanate reactive groups on the carbon black to the isocyanate groups of the polyurethane.
By providing the rubber reinforcing carbon black as a product of disintegration of compacted rubber reinforcing carbon black pellets, namely pulverized carbon black pellets, it is envisioned that isocyanate reactive surfaces of the rubber reinforcing carbon black can become created and exposed to better present and make available the aforesaid isocyanate reactive groups on the surface of the carbon black particles.
However, it is recognized that the rubber reinforcing carbon black of compacted carbon black particles normally inherently contains moisture adsorbed on its surface. The moisture is inherently reactive with the aforesaid excess isocyanate groups contained in an isocyanate/polymeric polyol based polyurethane reaction mixture and thereby significantly interferes with, and perhaps negates, the aforesaid interaction of isocyanate reactive groups of the carbon black surface with isocyanate groups contained in the polyurethane reaction mixture and thereby prospective improvements in polyurethane physical properties.
For example, to reduce or eliminate moisture from the carbon black granules, the rubber reinforcing carbon black pellets may be heated, for example, to at least about 104° C. for a suitable period of time hours followed by cooling to room temperature under a dry nitrogen atmosphere.
A desiccant such as dry molecular sieves may be blended with one or more of the pulverized rubber reinforcing carbon black granules (e.g. heat treated pulverized carbon black granules with reduced moisture content) and polymeric polyol to further remove moisture or prevent moisture interference from the rubber reinforcing carbon black granules as well as the polymeric polyol.
Therefore, in one embodiment of the invention, a desiccant in a form of dried molecular sieves is mixed with the dried disintegrated rubber reinforcing carbon black particles prior to introduction into the polyurethane reaction mixture (e.g. by pre-blending with the polymeric polyol of the polyurethane reaction mixture) to promote moisture free disintegrated rubber reinforcing carbon black particles.
The molecular sieve-containing product of the pulverized rubber reinforcing carbon black and polyol may then be mixed with the polyisocyanate to create the polyurethane reaction mixture and, ultimately, the polyurethane product of the reaction mixture which will contain the molecular sieves.
Rubber reinforcing carbon blacks are referenced, for example, in The Vanderbilt Rubber Handbook, 13th edition, (1991), Pages 397 through 419, and presented on Pages 417 and 418 with associated ASTM designated N numbers together with their Iodine adsorption and DBP (dibutylphthalate) number characterizations. The particle size and structure of the carbon black play a significant role, perhaps even a major role, in its dispersability in a polymer matrix and associated reinforcing properties. For example, smaller sized particles having greater surface areas (e.g. greater iodine adsorption values, g/kg, ASTM D1510) with large structure (e.g. significant dibutyl phthalate adsorption values, cc/100 g, ASTM D2414) tend to be very reinforcing but sometimes difficult to disperse in a polymer matrix. Larger sized particles, with thereby less relative surface area, with similar structure tend to be more easily dispersible in a polymer matrix but less reinforcing.